The present invention relates to an apparatus and a method for reproducing an image. More particularly, it relates to an apparatus and a method for reproducing an image of interest by displaying scaled-down images created from images and selecting one or more of the images from the scaled-down images.
In the past, many methods have been proposed for reproducing an image of interest rapidly by displaying scaled-down images (thumbnail images) created from a first frame image in each scene or the like as an index for searching the image of interest.
Alternatively, in order to display thumbnail images as an index for searching the image of interest, a method for recording an image has been known in which brightness histograms are taken of plural frames forming a moving image on recording images (moving images); if the difference in the histograms between a current frame and a previous frame exceeds a predetermined threshold value, it is determined that the scene has been changed, and thumbnail images are generated from frames representative of the scene and the thumbnail images are recorded with their scene change points.
When reproducing the images recorded on a recording medium, such as a digital versatile disc (DVD), as content according to the past image-recording method, each image is reproduced starting at the scene change point corresponding to a start point of the scene if a thumbnail image for the scene of interest is selected from among plural thumbnail images which are reproduced and displayed as an index for searching the image of interest. Thus, simply selecting the thumbnail image allows the scene of interest to be viewed from its start point, thereby grasping the content in the scene (see Japanese Patent Application Publication No. 2002-27411).
As shown in FIG. 1, thumbnail images Th, each for searching the image of interest, and a reproduced image M11 are displayed on the same screen with each of the thumbnail images Th and the image M11 being synchronized with each other, so that scenes before and after the reproduced image M11 can be viewed preceding a fast-forward or reverse movement, thereby making it convenient for a user to perform the fast-forward or reverse movement. In a case where an image is reproduced, as shown in FIG. 1, even if the image M11 is being reproduced by selecting the thumbnail image Th11, it is possible to change the reproduction start point promptly by selecting the thumbnail Th12, for example. Thus, any scene recorded before the reproduced image M11 has been recorded can be reproduced and displayed rapidly, thereby enhancing its convenience.
Processing in an application such that an image (a video image) and the thumbnail images in content are displayed in synchronization with each other places a large load on a CPU. This may require a CPU having a fast operating speed. An embedded apparatus in which a device for recording/reproducing an image (for example, a video device) is incorporated in a television receiver or the like often uses a CPU having a relatively slow operation speed. Thus, it may be difficult to reproduce and display all the thumbnail images, which have been recorded in a recording medium as content together with the video images, with each of the thumbnail images being synchronized with the video image.
If a CPU having a relatively slow operating speed is used, it is necessary to take processing time of about one second in order to reproduce and display thumbnail images each having 100 pixels. Thus, when reproducing and displaying the thumbnail images by taking the horizontal scanning direction of an image display screen as a time axis, it is possible to display five through seven thumbnail images with each of them being synchronized with the video image if each thumbnail image has about 120 pixels.
FIG. 2 shows a graph G10 where a fixed threshold value is set for selecting the number of thumbnail images capable of being displayed from all of the recorded thumbnail images. In FIG. 2, the horizontal axis is taken as time T and the vertical axis is taken as the difference in brightness histogram between the current frame and the previous frame so that the differences between scene change points are illustrated.
If, for example, six thumbnail images capable of being displayed are selected from all of the thumbnail images recorded as content during the time T, it is conceivable that a fixed threshold value TF is set for the differences in the brightness histograms in the graph G10 of FIG. 2, and the thumbnail images Th13 through Th18 corresponding to the differences D13 through D18 that exceed the fixed threshold value TF are extracted. Avoiding the reproduction and display of the thumbnail images corresponding to the differences that do not exceed the fixed threshold value TF enables a reduction in the number of the thumbnail images capable of being displayed on the screen with each of them being synchronized with the video image. This allows the load on the CPU to be decreased.
If, however, a fixed threshold value TF is set over all of the content to limit the number of thumbnail images, the content may include a section A in which there are only low difference values (scene change levels) and a section B in which there are high difference values, as shown in FIG. 2. The thumbnail images can be extracted from section B, but no thumbnail images can be extracted from section A. Therefore, as shown in FIG. 3, when reproducing and displaying the thumbnail images for the time length T corresponding to a horizontal frame length of the display screen, the thumbnail images Th13 through Th18 are densely displayed in a latter half of the time length T.
When many scene changes occur so that plural thumbnail images can be displayed in a short time, the thumbnail images may be overlapped with each other. Thus, thumbnail images such as Th13, Th14, Th15, and Th17 may be only partially displayed. In particular, it may be difficult to grasp the contents of the scene from the thumbnail image, like the thumbnail image Th15, a large part of which is covered by the other thumbnail image Th16, and select the scene of interest.
If a single fixed threshold value TF is set, the number of thumbnail images to be displayed can be reduced during a period of time when the scenes are changing frequently so that the load on the CPU can be reduced. During a period of time when the scenes are changing infrequently, no thumbnail image may be displayed according to the level of the fixed threshold value TF, although it may be possible to display a large number of thumbnail images based on the processing power of the CPU. Thus, because of an imbalance in the number of scene change points, there is an issue that an unevenness in the time to display the thumbnail images occurs.
It is desirable to present an apparatus and a method for reproducing an image or the like by which loads on the thumbnail image display processing is reduced and the unevenness in the time to display the thumbnail images because of an imbalance in the number of scene change points decreases.